The present invention relates in general to azo dyes, which are highly colored and thus useful in the dyeing of textiles (fabrics, fibers, yarns, and the like) hereinafter referred to as substrates. More particularly, the present invention represents an important step in the evolution of lightfast, and preferably also washfast, black dyeings on natural substrates (for instance, protein substrates such as wool, leather, and silk) and on synthetic substrates (for instance, nylon which is a synthetic polyamide), as it pertains to the preparation and use of 1:2 Iron (hereinafter Fe) complexes of ortho,ortho'-bis(hydroxy)-substituted monoazo dyes as environmentally friendly viable alternatives to black dyeings derived from 1:2 metal complexes of ortho,ortho'-bis(hydroxy)-substituted monoazo dyes based on metal ions, such as chromium (hereinafter Cr) ions, which are presently regarded by the United States Regulatory Authorities as priority pollutants.
By "environmentally friendly" or "environmentally safe" is meant that the Fe complexed azo dyes, the process of making the dyes, the dyes in substrates dyed with the dyes, and the process of dyeing substrates with the dyes do not produce in wastewater high levels of metal cations regarded as priority pollutants that eventually end up polluting streams, lakes, and rivers. In other words, Fe cations, which are needed by the human body, are not considered toxic, so that there is little or no pollution problem from the manufacture and use of the Fe complexed azo dyes. Recently, it has become evident from the open literature that the presence of color and priority pollutants in industrial wastewaters continues to be a subject of considerable concern. This presence of color and priority pollutants especially causes concern in the textile and dyestuffs industries, where such pollutants arise from the manufacture and use of lightfast metallized Cr, cobalt (hereinafter Co), or copper (hereinafter Cu) complexed azo colorants for natural and synthetic substrates.
By way of background, it is noted that over the years azo dyes metallized with Cr, Co, or Cu ions have become increasingly commercially important in the dyeing of textiles because the dyed textiles showed better lightfastness, rubbingfastness, and washfastness than textiles dyed with the corresponding chemical structural analogues that are unmetallized azo dyes. In particular, metallized azo dyes derived from ortho,ortho'-bis(hydroxy) monoazo dyes constitute an important class of colorants for the dyeing of wool and nylon for applications requiring high stability to prolonged and repeated exposure to ultraviolet radiation, to alkaline media, and to washings. In the case of fast and bright dyeings on wool, chromium has long been believed to be by far the best metal to use in complexing with azo dyes, as other metals have produced metallized azo complexes having inferior fastness to light and washing. For a general discussion of better lightfastness with metallized dyes as compared to unmetallized dyes, see for instance, Crossley, "Metallized Azo Dyes" American Dyestuff Reporter, Vol 27, No. 38, pp. 124-129 (December, 1938) and Crossley, "Metallized Acid Azo Dyes" American Dyestuff Reporter Vol. 28, No. 18, pp. 487, 488, and 492 (September, 1939).
The first Cr complexes of azo dyes that were developed were actually generated directly on wool fibers by the afterchrome mordant method, discussed in Welham, "Advances in the Afterchrome Dyeing of Wool", JSDC, Vol. 2, pp. 126-131 (April, 1986). This method, created in the 1920's, involves applying appropriately substituted unmetallized azo dyes to wool followed by treating the resultant dyed substrate with Cr(VI) or Cr(III) salts to produce the final color. This method led to the development of unmetallized azo dyes such as C. I. Mordant Black 11, a high volume dyestuff for the afterchrome mordant production of deep colors (for instance, black or grey) on wool where the amount of dye used is large, and where fast dyeings and an economical price are needed. C. I. Mordant Black 11 is illustrated in FIG. 1 of Welham, and is the isomer of the azo dye designated below as Dye 11.
Although this afterchrome mordant method improved the lightfastness and wetfastness of the dull alkali-sensitive dyeings obtained using the metal-free dyes, the method nevertheless afforded wastewater effluents from dye houses containing levels of metal ions deemed harmful to the environment. During the last few decades, when methods for solving environmental concerns arising from afterchrome dyeing were being pursued, it was widely believed, as espoused in the two Crossley articles mentioned above, that Fe azo complexes were so inferior to Cr azo complexes in both fastness and brightness that they could not be seriously considered as viable alternatives. Perhaps this is because in general the early complexes made were actually 1:1 Fe complexed azo dyes rather than the more desirable 1:2 Fe complexed azo dyes of the present invention. This belief in inferiority in turn probably led scientists away from Fe azo complexes as a method for the environmentally friendly application of metallized dyes to wool and nylon.
Thus, primarily as a step-saving way to achieve the good fastness achieved by afterchrome dyeing, the development in the 1930's of a method for dyeing textiles with metallized dyes in which the metal was inserted into the azo dye ligand prior to dyeing the substrate focused on Cr as the metal. Thus, Mordant Black 11 evolved into Cr premetallized azo dyes such as Acid Black 52 and Acid Black 172, which have the following structures designated as dye 2 and dye 3, respectively, ##STR1## and such as Acid Black 107. As that work unfolded, it was determined that the 1:2 premetallized Cr dyes were preferred over the corresponding 1:1 Cr complexes because the acidic pH required to apply the 1:1 Cr complexed azo dyes damaged wool. Interestingly, it was also determined that the toxicity level of residual Cr ion residues from exhausted premetallized dye baths was often greater than that observed in exhausted afterchrome dye baths when a method for reducing residual Cr ions in the latter type of dye bath was employed.
In short, using Cr metallized dyes did not obviate the problem of Cr(VI) and/or Cr(III) in effluent from the dyeing process, which is especially of concern when Cr(VI) is used, as hexavalent chromium is toxic to many forms of aquatic life as well as to the organisms employed to degrade sewage in biological degradation facilities. This concern has led environmental authorities to discourage the continued use of dyeing with both premetallized Cr azo dyes and afterchrome dyes, and to impose severe limitations on the concentration of both Cr(VI) and Cr(III) in effluents. Efforts to comply with these demands led in turn to the development of wastewater treatment methods for lowering Cr ion levels prior to discharging an exhausted dye bath. Typical methods employed include precipitation of the metal followed by collection by filtration, and include reduction of residual Cr(VI) to Cr(III) followed by complexing the resultant Cr(III) ions in situ and absorbing them onto the dyed wool fiber.
Also as further discussed below in connection with the preparation of Acid Black 172 (the Cr complexed azo dye designated above as dye 2), the synthesis of Mordant Black 1 (the unmetallized precursor for making Acid Black 172 and designated below as dye 11) requires copper sulfate. Thus, the manufacture of these dyes produces Cu ion, another priority pollutant in effluent wastewater, resulting in a double pollution problem from the Cu ions produced in the manufacture of these dyes and from the Cr ions produced in the application of these dyes.
Also, it is noted that the metallized Cr dyes themselves can decompose resulting in metal cations being released into rinse water when dyed fabric is washed. For a discussion of the decomposition of Cr complexed azo dyes, see for instance, Gorzka et al., "Investigations On Kinetics of Decomposition of Chromium Complex Dyes of 1:2 and 1:1 Types" Dyes and Pigments, Vol. 5, pp 263-275 (1984).
Environmental considerations aside, one of the most important considerations in determining the suitability of dyestuffs for specific applications is lightfastness. Dyes tend to undergo photodegradation upon exposure to light, especially light in the ultraviolet spectrum, resulting in fading of the dyed textile fibers. Automobile upholstery fabrics (including the leather used in expensive automobiles) are used in perhaps one of the most severe and demanding environments for dyestuffs. Automobile interiors may be exposed to direct sunlight over extended periods of time, and may encounter extremely high temperatures and humidities. Also, since people continually move in and out of automobiles, the dye in the automobile upholstery fabrics should not rub off onto clothing. Consequently, automobile upholstery fabrics require good rubbingfastness properties, as well as good lightfastness properties. Most of the dyestuffs presently available, other than the Cr complexed azo dyes, do not provide this high level of these properties demanded in automotive applications, especially where relatively dark colors are required.
The Fe complexed azo dyes of the invention are black, although the corresponding commercial Co structural analogues are red or blue. Examples are Acid Red 182 and Acid Blue 171. Moreover, although Fe complexed azo dyes are expected to have poor lightfastness as compared to Cr complexed azo dyes, as discussed above in connection with the two Crossley articles, the lightfastness properties, and preferably also the rubbingfastness properties, of the black Fe complexed azo dyes of the invention were unexpectedly found to be superior for use on wool and nylon, comparable to those properties in commercially available black 1:2 Cr complexed azo dyes. Thus, the black Fe complexed azo dyes of the invention can be substituted for the black Cr complexed azo dyes, which are among the commercial dyes used for automobile upholstery, but have the drawback of being based on a priority pollutant that is among the most notorious of priority pollutants producing cation contaminants which happen to be very toxic to the human body. Thus, the use of Cr metal ions may be obviated with the present invention.
Obviating Cr metal ions has become increasingly important because the wastewater clean up has become very costly, particularly due to the energy costs resultant from the needed treatment of the wastewater to remove metal cations regarded as toxic. There are four main ways to remove these metal cations, (1) reducing Cr(VI) to Cr(III) followed by complexing the Cr(III) to fabric dyed with a mordant dye, (2) flocculation, (3) ion exchange, and (4) electrolysis, and each is very expensive. Moreover, with (2), (3), and (4) once the metal cations are removed from the wastewater, the resultant is sludge. Now the sludge has to be either put into a landfill or incinerated. If the sludge is put into a landfill, the landfill can end up in a Superfund clean up, another cost. On the other hand, if the sludge is incinerated, the resultant ash, which still contains the priority pollutant, has to go into a landfill, and again the landfill can end up in a Superfund clean up. In contrast, energy is saved with the manufacture and use of the Fe complexed azo dyes of the present invention by not having to do the wastewater cleanup necessitated by the manufacture and use of the Cr complexed azo dyes.
Thus, as can be seen from the above discussion, the formation of metal complexes of azo dyes has figured prominently in dyestuffs chemistry. In addition, a general background discussion of medially metallized azo dyes, where chromium (III), cobalt (III), and copper (II) are the three metal ions used in commercial metal complex azo systems is contained in Gordon and Gregory, "Metal Complex Azo Dyes" Organic Chemistry in Color, pp 116-121 (1983).
Of course, many patents and published patent applications also discuss metallized azo dyes. More particularly, Tzikas U.S. Pat. No. 4,963,659 (1990) and U.S. Pat. No. 5,084,562 (1992), both assigned to Ciba-Geigy, require a 1,3,5-triazine system in the dye, but the presence of a metallized azo system in the dye is only optional. U.K. Patents 743,907 (1956) and 774,035 (1957) and Canadian Patents 543,916 (1957) and 560,031 (1958) disclose a reduction to practice of only Cr metallized azo dyes and Co metallized azo dyes. General Aniline & Film German Patent 1,120,041 (1961) and Conrad U.S. Pat. No. 2,499,133 (1950), assigned to Allied Chemical and Dye, disclose a reduction to practice of only Cr metallized azo dyes.
Although Fe salts are not only cheaper than Co and Cr salts but also are potentially more environmentally safe, nevertheless, there do not appear to be many Fe complexed azo dyes that are widely used in the textile industry. Thus, interestingly, very little has been published about the suitability for dyeing textiles with Fe azo complexes as potential alternatives to currently used azo dyes metallized with chromium (VI), chromium (III), or cobalt (II) salts.
However, some patents and published patent applications do disclose a reduction to practice of certain Fe complexed azo dyes. One patent is U.S. Pat. No. 4,732,573 (1988) to Hohmann et al., assignors to Hoechst, which only discloses certain Fe complexed azo dyes in which the azo group is not a coordinating ligand. Instead, the Fe atom is part of an anionic moiety that serves as the counterion for the cationic group in the dyes disclosed. In addition, the disclosed dyes are cationic dyes for the coloration of polyacrylonitrile.
An Fe complex of an azo dyestuff having a nitrophenol moiety was made in U.S. Pat. No. 2,120,799 (1935) to Crossley et al., assignors to Calco Chemical. This Fe complexed azo dyestuff, called Acid Brown 98 (a leather dye), is one example of an Fe azo complex used in textile dyeing. This 1:1 Fe azo complex has the following structure: ##STR2##
Also, an Fe complex of an azo dyestuff somewhat similar in structure to Acid Brown 98, but instead having the SO.sub.3 H attached to the same phenyl ring as the NO.sub.2 and having phenyl instead of methyl attached to the 3-position of the pyrazolone ring, was made in U.S. Pat. No. 3,432,393 (1969) to Klein, assignor to GAF Corporation, for use on leather.
Also, one example of a yellow-brown 1:2 iron complex of disazo dye for application to leather disclosed in the Berenguer et al. Published Patent Applications DE4133166-A and DE413367-A, is designated as follows: ##STR3##
Other patents and published patent applications which disclose a reduction to practice of certain Fe complexed azo dyes are U.S. Pat. No. 4,120,854 (1978) to Wicki, assignor to Sandoz, U.S. Pat. No. 4,547,566 (1985), U.S. Pat. No. 4,563,520 (1986), and U.S. Pat. No. 4,638,055 (1987), all to Bergmann et al,, assignors to BASF, U.S. Pat. No. 5,104,979 (1992) to Hansen et al., assignors to BASF, and German Published Patent Application Nos. DE 4,133,166-A (1992) and 4,133,167-A (1992), both Berenguer et al., assignors to Sandoz. However, all of these patents and published patent application disclose only polyazo dyes, such as disazo, trisazo, or tetrakisazo.
Also, an English language abstract of Niimura et al. Japanese Published Patent Application No. 62-129358-A (published Jun. 11, 1987) defines certain Fe azo compounds as being of the formula: ##STR4## where R.sub.1 and R.sub.2 are H, C.sub.1-18 alkyl, alkenyl, sulfonamide, or mesyl, and n and n' are 1 to 4, and A+ is H+, Na+, K+, NH.sub.4 +, aliphatic ammonium ion, alicyclic ammonium ion, or heterocyclic ammonium ion, for use as a toner for electrophotography. In the reduction of practice disclosed in the English language abstract, A+ is Na+, but (R.sub.1).sub.n and (R.sub.2).sub.n, are both Cl. Moreover, the English language abstract mentions nothing with respect to use of Fe azo compounds in dyeing textiles (the use of the inventive Fe dyes), but only mentions use as a toner for electrophotography.